1. Applicable Field of the Invention
This invention relates to a damper for a flapdoor using viscous fluid that comprises a high molecular viscous fluid such as polyisobutylene and a coil spring, wherein the resistance of the damper is obtained as a combined effect of the viscous shearing drag of the fluid and the righting force of the wound or unwound coil spring, said resistance being utilized as damping force to damp the torque load applied to the door when it is swung in one way, said door being lightly and easily swung in the other way due to the righting force of the coil spring and more particularly the present invention relates to a configuration of a coil spring to be used for such a damper both as a one-way clutch and as a power source.
2. Prior Art
FIGS. 6(a) and (b) of the accompanying drawings illustrative a conventional damper using viscous fluid, which comprises within a case a an externally rotatable shaft b, a given number of movable discs c, c', c" . . . perpendicularly and rigidly fitted to said rotary shaft b so that they are rotatable with said shaft b, another given number of fixed discs d, d', d" . . . arranged alternately with said rotatable discs c, c', c" . . . so that they are not rotatable with the rotary shaft b but longitudinally movable due to their engagement with the case a and a certain volume of viscous fluid e filling the space within the case a. An alternative conventional damper (not shown) may comprises movable discs which are not rigidly fitted to the shaft but longitudinally movable.
Either of the above described conventional damper can provide a damping effect against any external force that may be applied to the rotary shaft in the form of rotary force as a viscous shearing drag is generated between each of the movable discs c. c', c" . . . and adjacent one of the fixed discs d, d', d" . . . within the damper when the movable discs c, c', c" . . . that rotate with said rotary shaft are moved relative to the fixed discs d, d', d" . . .
3. Problem to be Solved by the Invention
With an arrangement as described above, however, there cannot be provided a variable resistance damper that produces different resistive forces, or damping forces, depending on the since of rotation (clockwise, counterclockwise) of the rotary shaft because it has a constant viscous shearing drag that between each of the movable discs c, c', c" . . . and the adjacent one of the fixed discs d, d', d" . . . that determines the resistant force of the damper.
Thus, when a damper having a configuration as described above is used for a flap-cover of a toilet stool or a flapdoor of a closet for example, where the rotary shaft of the damper is secured to the cover or the door whose axial torque shows a cosine load curve, its resistance will be significant if the cover or the door is rotated from a 0.degree. position to a 90.degree. position for opening (or closing). Therefore, a very complicated damping mechanism will be necessary if a door is required to be lightly opened and slowly and gradually closed.
In order to solve this problem, there has been proposed by the inventor of the present invention a damper for a flapdoor using viscous fluid comprising within a case a rotary shaft rotatable with the flapdoor, a movable members fitted to said shaft by way of a one-way clutch so that it can be rotated with the rotary shaft only in one sense, a coil spring arranged within said case in a state where it is wound to some extend under stress and viscous fluid filling the space within the case, the viscous shearing drag of the viscous fluid and the righting force of the wound coil spring being utilized for damping the movement of the rotary shaft.
While a flapdoor damper having a configuration as described above does not show any damping effect when the flapdoor is rotated from a 0.degree. position to a 90.degree. position, it effectively damps the rotary movement of the flapdoor when the door is rotated back from the 90.degree. position to the initial 0.degree. position, so that the door can be operated with a light, slow and smooth motion that can be controlled by way of the single rotary shaft.
The object of the present invention is to provide a flapdoor damper using viscous fluid at a reduced cost by incorporating a single coil spring that has a combined effect of the one-way clutch and the spring of the above described damper that functions as a power source so that it may be realized with reduced dimensions and a simplified configuration, while maintaining the performance of its predecessor model.